DERBY-6426 Fix isLoginException
code treats any StandardException as a login exception due to curious no-op code. Added login state check to make it work as expected. 

Contributed by Dave Brosius



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1550287 13f79535-47bb-0310-9956-ffa450edef68